1. Field of the Invention
The present invention applies to burst timing for radio communications systems and, in particular, to selecting from among different amounts of delay for use in sending a burst from one station to another.                2. Description of the Prior Art        
Mobile radio communications systems such as cellular voice and data radio systems typically have several base stations in different locations available for use by mobile or fixed user terminals, such as cellular telephones or wireless web devices. Each base station typically is assigned a set of frequencies or channels to use for communications with the user terminals. The channels are different from those of neighboring base stations in order to avoid interference between neighboring base stations. As a result, the user terminals can easily distinguish the transmissions received from one base station from the signals received from another. In addition, each base station can act independently in allocating and using the channel resources assigned to it.
Such radio communications systems typically include a broadcast channel (BCH). The BCH is broadcast to all user terminals whether they are registered on the network or not and informs the user terminals about the network. In order to access the network, a user terminal normally tunes to and listens to the BCH before accessing the network. It will then use the information in the BCH to request access to the network. Such a request typically results in an exchange of information about the network using separate control and access channels and ends in the user terminal receiving an assignment to a particular base station.
Before the user terminal has received an assignment, its request for access is typically sent in a timeslot that is shared with other user terminals. This allows for the possibility that its request will collide with other requests. If the request is received at the same time as the colliding request, it can be difficult to resolve the colliding requests at the base station. However, accurate delay timing advance or delay assignments cannot be made by the base station until the range to each of the user terminals is known. In addition, the BCH does not permit assignments to be made as it is the same for all user terminals that receive it.